Conventionally, disc-shaped optical information recording media have been widely used as optical information recording media, and CDs (Compact Discs), DVDs (Digital Versatile Discs), Blu-ray Discs (registered trademark, hereinafter called BDs), and the like are generally used.
On the other hand, in an optical disc device compatible with such optical information recording media, various types of content, such as music content and video content, or various types of information, such as various data for a computer, is recorded on an optical information recording medium. Particularly, in recent years, the amount of information has been increasing due to higher definition of images and higher sound quality of music, and also an increase in the number of pieces of content to be recorded on an optical information recording medium has been demanded. Thus, higher capacity has been demanded for optical information recording media.
Accordingly, an optical information recording medium has been suggested that is made by using a material for forming recording pits by causing a two-photon absorption reaction using light as a method for increasing the capacity of the optical information recording medium, whereby information is three-dimensionally recorded in the thickness direction of the optical information recording medium (e.g., see Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-37658
Incidentally, the two-photon absorption reaction is a phenomenon that occurs only using light of high intensity, and thus a light source achieving a high emission intensity needs to be used as a light source. As the light source, a short-pulse light source that outputs laser light in a short-pulsed manner, such as a so-called picosecond laser or femtosecond laser, is used. For example, a titanium sapphire laser and a YAG (yttrium aluminum garnet) laser are known.
However, in such a short-pulse light source, output of short pulses is realized by an operation of an optical component provided outside a light generator. Therefore, the short-pulse light source typically has a large size and a high price, and thus mounting it in an optical disc device is unpractical.
Here, if laser light can be output in a pulsed manner directly from a semiconductor laser, which is a compact light generator typically used in an optical disc device, it is unnecessary to provide an optical component outside the light generator, and the size of the short-pulse light source can be significantly reduced. When it is assumed that laser light can be output in a short-pulsed manner from a semiconductor laser, the semiconductor laser needs to be controlled so that laser light is output in a desired short-pulsed manner in accordance with application of voltage.